The viscosity of aqueous systems plays a decisive role for a multiplicity of applications. Thickener systems are therefore frequently used in water-based systems, such as, for example, well treatment fluids, cleaner compositions, detergents, formulations for the treatment of leather and textiles, hydraulic fluids, etc., in order to provide the rheological properties required for their specific applications.
WO 92/08753 discloses polymer compounds which are useful as thickeners for aqueous compositions and in particular for latex dispersions.
EP 0 225 661 describes the preparation of gels by crosslinking phosphate esters with polyvalent metal cations, in particular with aluminum ions.
WO 02/102917 describes aqueous compositions which comprise polymers having nonionic, ionic and hydrophobic functional groups, whose viscosity is increased under the action of shear forces or which form a gel under the action of shear forces.
WO 2005/071038 describes compositions and methods for shortening the recovery time of cationic, zwitterionic and amphoteric viscoelastic surfactant compositions after the action of shear forces by addition of three-block oligomers having hydrophilic and hydrophobic moieties, the surfactants preferably having a betaine structure.
US 2006/0128597 describes compositions and methods for shortening the recovery time of cationic, zwitterionic and amphoteric viscoelastic surfactant compositions after the action of shear forces by addition of partly hydrolyzed polyvinyl esters or partly hydrolyzed polyacrylates, the surfactants likewise preferably having a betaine structure.
US 2006/0111248 describes methods for shortening the recovery time of zwitterionic viscoelastic surfactant compositions after the action of shear forces by addition of compounds of the general formulaR-(EO)x(PO)y—R′—OHwhere R is a C3-C18-alkyl group, R′ is a C0-C14-alkylene group, EO is ethyleneoxy and PO is propyleneoxy, the surfactants preferably having a betaine structure.
U.S. Pat. No. 6,194,356 describes well treatment fluids which comprise a viscoelastic surfactant in combination with a crosslinkable, hydrophobically modified polymer.
U.S. Pat. No. 7,084,095 describes the use of encapsulated polymers in an aqueous composition comprising a viscoelastic surfactant, the polymer producing a change in the rheological properties of the aqueous composition under the conditions in the interior of the well.
WO 02/11874 discloses a viscoelastic well treatment fluid which comprise a sufficient amount of an oligomeric surfactant for controlling the viscoelastic properties of the fluid. The monomers of the surfactant used are ionic or zwitterionic compounds which have at least one charged head group and one long-chain hydrophobic hydrocarbon radical.
WO 03/056130 describes aqueous viscoelastic fluids for breaking open rock formations, which comprise a viscoelastic surfactant, especially a betaine, and a hydrophobically modified polymer, the polymer preferably having a molecular weight in the range from 104 to 107 g/mol.
WO 2005/040554 describes methods for increasing the viscosity of viscoelastic surfactant compositions for the treatment of wells by addition of hydrophilic-lipophilic organic compounds, such as, for example, alkyl alcohols, alkylthiols or alkylamines.
In many of the possible fields of use of thickener systems, the high viscosity of the aqueous compositions which is required for the special application prove to be problematic, for example in the placing or the subsequent removal of the composition. Particularly in the treatment of poorly accessible areas with relatively high-viscosity compositions, it is desirable to be able to reduce the viscosity of the composition after treatment is complete, in order to facilitate complete removal of the composition. An example of this is in particular the use of relatively high-viscosity treatment fluids in the development and maintenance of wells.
For these applications and a multiplicity of other applications, it is advantageous to use compositions whose viscosity can be varied by a simple method. None of the abovementioned documents describes such compositions which make it possible to vary the viscosity under the respective conditions of use.